logswitch_finish()
Attempt to finalize a log table switch in progress
return values:
-1 if switch in progress, but not complete
0 if no switch in progress
1 if performed truncate on sl_log_2
2 if performed truncate on sl_log_1

DECLARE
v_current_status int4;
v_dummy record;
v_origin int8;
v_seqno int8;
v_xmin bigint;
v_purgeable boolean;
BEGIN
-- ----
-- Get the current log status.
-- ----
select last_value into v_current_status from sl_log_status;
-- ----
-- status value 0 or 1 means that there is no log switch in progress
-- ----
if v_current_status = 0 or v_current_status = 1 then
return 0;
end if;
-- ----
-- status = 2: sl_log_1 active, cleanup sl_log_2
-- ----
if v_current_status = 2 then
v_purgeable := 'true';
-- ----
-- Attempt to lock sl_log_2 in order to make sure there are no other transactions
-- currently writing to it. Exit if it is still in use. This prevents TRUNCATE from
-- blocking writers to sl_log_2 while it is waiting for a lock. It also prevents it
-- immediately truncating log data generated inside the transaction which was active
-- when logswitch_finish() was called (and was blocking TRUNCATE) as soon as that
-- transaction is committed.
-- ----
begin
lock table sl_log_2 in access exclusive mode nowait;
exception when lock_not_available then
raise notice 'Slony-I: could not lock sl_log_2 - sl_log_2 not truncated';
return -1;
end;
-- ----
-- The cleanup thread calls us after it did the delete and
-- vacuum of both log tables. If sl_log_2 is empty now, we
-- can truncate it and the log switch is done.
-- ----
for v_origin, v_seqno, v_xmin in
select ev_origin, ev_seqno, "pg_catalog".txid_snapshot_xmin(ev_snapshot) from sl_event
where (ev_origin, ev_seqno) in (select ev_origin, min(ev_seqno) from sl_event where ev_type = 'SYNC' group by ev_origin)
loop
if exists (select 1 from sl_log_2 where log_origin = v_origin and log_txid >= v_xmin limit 1) then
v_purgeable := 'false';
end if;
end loop;
if not v_purgeable then
-- ----
-- Found a row ... log switch is still in progress.
-- ----
raise notice 'Slony-I: log switch to sl_log_1 still in progress - sl_log_2 not truncated';
return -1;
end if;
raise notice 'Slony-I: log switch to sl_log_1 complete - truncate sl_log_2';
truncate sl_log_2;
if exists (select * from "pg_catalog".pg_class c, "pg_catalog".pg_namespace n, "pg_catalog".pg_attribute a where c.relname = 'sl_log_2' and n.oid = c.relnamespace and a.attrelid = c.oid and a.attname = 'oid') then
execute 'alter table sl_log_2 set without oids;';
end if;
perform "pg_catalog".setval('sl_log_status', 0);
-- Run addPartialLogIndices() to try to add indices to unused sl_log_? table
perform addPartialLogIndices();
return 1;
end if;
-- ----
-- status = 3: sl_log_2 active, cleanup sl_log_1
-- ----
if v_current_status = 3 then
v_purgeable := 'true';
-- ----
-- Attempt to lock sl_log_1 in order to make sure there are no other transactions
-- currently writing to it. Exit if it is still in use. This prevents TRUNCATE from
-- blocking writes to sl_log_1 while it is waiting for a lock. It also prevents it
-- immediately truncating log data generated inside the transaction which was active
-- when logswitch_finish() was called (and was blocking TRUNCATE) as soon as that
-- transaction is committed.
-- ----
begin
lock table sl_log_1 in access exclusive mode nowait;
exception when lock_not_available then
raise notice 'Slony-I: could not lock sl_log_1 - sl_log_1 not truncated';
return -1;
end;
-- ----
-- The cleanup thread calls us after it did the delete and
-- vacuum of both log tables. If sl_log_2 is empty now, we
-- can truncate it and the log switch is done.
-- ----
for v_origin, v_seqno, v_xmin in
select ev_origin, ev_seqno, "pg_catalog".txid_snapshot_xmin(ev_snapshot) from sl_event
where (ev_origin, ev_seqno) in (select ev_origin, min(ev_seqno) from sl_event where ev_type = 'SYNC' group by ev_origin)
loop
if (exists (select 1 from sl_log_1 where log_origin = v_origin and log_txid >= v_xmin limit 1)) then
v_purgeable := 'false';
end if;
end loop;
if not v_purgeable then
-- ----
-- Found a row ... log switch is still in progress.
-- ----
raise notice 'Slony-I: log switch to sl_log_2 still in progress - sl_log_1 not truncated';
return -1;
end if;
raise notice 'Slony-I: log switch to sl_log_2 complete - truncate sl_log_1';
truncate sl_log_1;
if exists (select * from "pg_catalog".pg_class c, "pg_catalog".pg_namespace n, "pg_catalog".pg_attribute a where c.relname = 'sl_log_1' and n.oid = c.relnamespace and a.attrelid = c.oid and a.attname = 'oid') then
execute 'alter table sl_log_1 set without oids;';
end if;
perform "pg_catalog".setval('sl_log_status', 1);
-- Run addPartialLogIndices() to try to add indices to unused sl_log_? table
perform addPartialLogIndices();
return 2;
end if;
END;